New package: FITSHeaders v0.4.0

[JuliaRegistrator]

• Registering package: FITSHeaders
• Repository: https://github.com/emmt/FITSHeaders.jl
• Created by: @emmt
• Version: v0.4.0
• Commit: 6534d3e85b5a733630991929c7cec8ce3bdbbab5
• Reviewed by: @emmt
• Reference: emmt/FITSHeaders.jl@6534d3e#commitcomment-141591533
• Description: A pure Julia package for managing FITS header records.
• Release notes:

- Package renamed as `FITSHeaders` (as suggested [here](https://github.com/JuliaRegistries/General/pull/105900#issuecomment-2085455856)).
- Undefined FITS card value is `undef` (was `missing`). When creating a FITS card, `missing` is considered as `undef`.
- Comparison operators (`==`, `!=`, `<`, `>`, `≤`, and `≥`) can be applied to FITS card values. The other operand may also be a card value.
- Logical value stored as an integer in `FitsCard`. This is an internal change

[github-actions]

Your new package pull request met all of the guidelines for auto-merging and is scheduled to be merged when the mandatory waiting period (3 days) has elapsed.

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[emmt]

[noblock]
This new package is a renaming of BaseFITS as suggested here by @LilithHafner.